How do I change the radius for proportional editing WITHOUT PgUp/PgDn?
If you have trouble using the standard keyboard shortcuts you can adjust your settings to suit your keyboard.

In File->User Preferences under the Input tab you will find a group called Transform Modal Map, under which you will find the shortcut settings to adjust proportional influence. You can adjust these to anything that works for you, be sure to Save User Settings so that the changes are available every time you start blender.